A team of Health Department doctors is closing in on what caused four Staten Islanders to be stricken with encephalitis or an encephalitis-like virus.

While one person was released from Staten Island University Hospital on Saturday after being treated for what was determined to be meningitis, four others are still seriously ill, said Sandra Mullin of the city’s Department of Health and Mental Hygiene.

Doctors so far have determined the cause of the encephalitis-like disease that struck two patients – although they wouldn’t say what it was.

The other two patients have been diagnosed with encephalitis. They tested negative for West Nile and Eastern Equine viruses, which can cause encephalitis, Mullin said.

Between late September and early October, the five patients, ranging in age from 22 to 54, began showing symptoms of an encephalitis-type virus, including fever, headache and fatigue.